1. Field of the Invention
The invention relates to collimators for use with DWDM multiplexors or demultiplexors, and particularly to dual fiber collimators with V-groove positioning devices.
2. The Related Art
As well known, Dense-Wavelength-Division-Multiplexing(DWDM) multiplexors or demultiplexors generally use the optical filter and the fiber optic collimators. Understandably, the collimator(s) used in DWDM applications may be called DWDM collimators specifically to distinguish from other collimators having other usages. In these applications, a band-pass optical filter is employed to multiplex or demultiplex a desired transmission channel of the in-and-out light of the system according to its center wavelength. An international standard wavelength grid has been suggested by International Telecommunication Union (ITU) for the center wavelengths of the DWDM channels. In the DWDM application, the center wavelength of the DWDM optical filter which does not coincide with the ITU standard wavelength, should be tuned to comply therewith. As the center wavelength of the band-pass optical filter depends upon the incident angle of the light that propagates therein, the center wavelength of the band-pass optical filter can be tuned by such an incident angle. The prior art generally uses an Y-branch structure of the three conventional fiber optic collimators wherein the incident angle is tuned by changing the angles between the collimators and thus the center wavelength of such a multiplexor/demultiplexor is adjustably coincident with the desired ITU wavelength. The disadvantage of such design includes difficulties in reducing its size to achieve a robust and compact structure. The related matters may be referred to U.S. Pat. Nos. 4,464,022, 5,204,771, 5,574,596 and 5,845,023, and xe2x80x9ccompact Polarization-Independent Optical Circulatorxe2x80x9d, Applied Optics, Vol. 20, No. 15, August 1981, pp.2683-2687.
Therefore, it is desired to provide a collimator, for use with DWDM applications, with means which can precisely and efficiently have the filter and the corresponding collimated beam with a required incident angle, thus assuring a desired ITU wavelength can be obtained.
According to an aspect of the invention, a V-groove dual fiber collimator including an optical lens and a V-groove dual fiber ferrule means fixed with each other. The ferrule means includes a V-groove base chip and a cover chip commonly enclosed by a protective guiding sleeve wherein two pigtail fibers are respectively received within the corresponding grooves of the V-groove chip. The V-groove ferrule means is itself fixed by adhering its own internal components and the corresponding embedded fibers, and also fixed to the lens by adhesive.
Another feature of the invention is to specifically provide a V-groove dual fiber DWDM collimator having the DWDM filter thereof, in which the center wavelength of the DWDM filter could be easily tuned to coincident with the predetermined desired ITU wavelength.
Yet another feature of the invention is to provide a new method/procedure to assemble the filter-lens and the ferrule means in a DWDM collimator, by providing a dense series of ferrule means including different spacing between the corresponding dual fibers thereof, to comply the filter center wavelength with the ITU grid. To achieve a specific channel, first a proper DWDM filter is picked and fixed with the lens, then a specific ferrule means among such dense series, which may almost precisely offset the original deviated center wavelength of the picked DWDM filter to the desired position compliant with the ITU, is selectively to be assembled to the picked filter-lens, thus precisely obtaining the desired DWDM collimator.